Folded-line reverberation device



Jan. 9, 1968 H. E. MEINEMA 3,363,202

FOLDED-LINE REVERBERATION DEVICE Filed Dec. 9, 1966 FIG.!

HERBERT E. MEINEMA ATTORNEYS INVENTOR United States Patent Q 3 363,262 FGLDEFCt-HNE RETERBERATHGN DEVICE Herbert E. Meinema, RD. 1., Box 62, Earboursville, Va. 22923 Filed Dec. 9, 1966, Ser. No. 604,110 6 Claims. (Cl. 333-30) ABSTRAQT F THE DHSCLQSURE This disclosure sets forth an artificial reverberation line which transmits audio Waves in a rotational or torsional mode through a coiled spring by means of transducers at opposite ends of the line. The coiled spring is folded sharply at an intermediate positionto provide two substantially parallel portions and thus placing the two transducers at substantially adjacent positions. A single support member engaging the fold in the coil spring provides a damping compliance reducing compressional mode flutter along both portions of the spring. An intercoupling member in the coil spring on both sides of the fold is provided with a thin planar member having stiffness in its plane against rotational motion, thereby transmitting the rotational mode energy from one line portion around th fold and back into the other line portion.

Background of invention This invention relates generally to apparatus for producing time delays in electrical audio signals to provide synthetic acoustic reverberation devices employing a coiled spring delay line member operable in a rotational mode of wave transmission from a transmitting transducer at one end of the line to a receiving transducer at the other end of the line.

This general type of coiled spring reverberation device operating in the rotational mode is described in the H. E. Meinema et al. Patent 2,982,819, issued May 2, 1961, which is representative of the state of the prior art. However, there are several disadvantages in the prior art devices.

One significant shortcoming is the large amount of space required since long coil springs are necessary to get reasonable delays suggesting large auditorium characteristics, While the patented structure may appear to be a partially folded delay line, actually it has linearly disposed lines in which the normal sag has been increased so as to assume a catenary shape and thus is an improvement over linearly disposed lines. Because of this the structure must always be mounted in a vertical plane and any displacement such as caused by a small physical shock causes the springs to sway and bump against the mounting structure thus producing very loud banging noises in the acoustical output system. Also, it is necessary to wind the springs with considerable spacing between adjacent turns to prevent rubbing as the only force acting to elongate the springs is that due to gravity and this, of course, is not uniform throughout the length of the suspended spring, being greatest at the spring ends and almost zero at the bottom of the caternary. It was not known how to fold the lines back alongside each other so that the two portions became substantially parallel to significantly reduce the space required. This is particularly important, for example, when such lines are used in automobile sound systems where space limitations are severe.

These prior art devices also have used two or more lines with different effective lengths in order to provide more uniform frequency response characteristics. This adds expense in the requirement for multiple transducers and multiple lines, and preferably the same effective response characteristic should be afforded more efliciently with a single line.

Summary of the invention A general object of this invention is to provide an improved coil spring reverberation device.

It is therefore an object of this invention to provide a more compact reverberation delay line with two coil spring portions folded back from an intermediate point to lie substantially parallel to each other.

Another object of the invention is to provide means of damping compressional mode flutter in a coil spring delay line operating in the rotational mode of wave transmission.

Yet another object of the invention is to provide more uniform frequency response from a single coiled spring delay line operating in a rotational mode with transducers at opposite ends of the line.

Still another object of the invention is to provide an improved reverberation delay line giving good signal to noise ratios over a Wide audio frequency spectrum.

Accordingly, a delay line afforded by this invention takes the form of a coiled spring member operating in the rotational mode of wave transmission and folded at an intermediate position to form two substantially parallel spring portions with transducers at each end of the line positioned substantially adjacent each other, and having a support device engaging the spring member at the fold.

The support device is made to exert a bi-directional A force substantially along the axes of both spring portions with a compliance of proper magnitude to substantially damp the compressional mode flutter along the axes of both lines. Thus, the line portions on either side of the fold need not be equal in length and counter-wound, so that the two line portions may have different effective lengths to thereby produce the more uniform frequency response effect in a single line which formerly required two separate lines of different length.

The rotational wave transmission energy is transmitted from one line portion around the support into the remaining line portion by means of a thin planar section such as a zig-zag spring which substantially matches the line impedance but is stiff to the rotational energy in the plane of the member. This member then pivots freely about the support member and may be coupled thereto by an intermediate wire or coil spring member providing rotational compliance between the coil spring portions and the support. This latter member has a rotational compliance of less magnitude than that of the coil spring.

Rigid coupling between each coil spring portion and the planar member effects translation of the rotational wave transmission energy through the planar member which pivots about the support by means of the crotch of a substantially V-shaped coupling section of the planar member.

Thus, the present invention provides an improved, compact reverberation line with good frequency band uniformity and little flutter, yet simplified in form and less expensive to produce.

Drawing FIGURE 1 is a top View of a folded delay line constructed in accordance with the teachings of this invention; and

FIGURE 2 is an enlarged side view of a compliance support member coupled to an intermediate point of the delay line at the fold.

Description As may be seen in the drawing, a delay line comprising a shorter arm portion ill and longer arm portion 12 of a coiled spring 13 is folded back upon itself sharply at the fold line 14 to provide in this embodiment the two substantially parallel or adjacent portions 19-12. More folds can be incorporated if desired. At each end of the delay line is a transducer 16, 17 comprising a rotary magnet-coil structure, which may be of conventional configuration. One of these transducers transmits a rotary wave motion into the coil spring 13, which provides a typical time delay of perhaps seventy milliseconds before the wave motion is received as rotary motion at the other transducer.

A folded acoustic line has only been afforded heretofore for compressional mode of operation, and even then required complicated lever arrangements as shown in the L. Hammond Patent 2,230,836. However, the rotational mode of wave transmission is preferred since springs which are operated in a pure rotational mode can be aifected but little by normal physical shock that takes the compressional mode and has only a small rotational mode component. However, the compressional mode wave motion may continue fluttering for a long time unless specific damping is required. As contrasted with prior art damping which comprised two equal length portions of line counterwound to cancel the compressional-to-rotational translation effect in the lines, the present embodiment uses a support member which has a compliance for damping the compressional mode flutter. Thus, the support member comprises here a member such as spring arm 21 which provides a bidirectional force substantially along the axes of the two spring portions 10, 12. This provides a damping action not only to the compressional waves but also for lateral spring motion, and limits the shock waves to a very few reflections, which as a practical matter are not disturbing to the ear when superimposed on an audio signal being transmitted through the line, even when the two portions 10 and 12 of the coil spring 13 are not counterwound.

This enables two two spring portions 10 and 12 to be of different effective length as shown to thereby provide for an improved band pass characteristic over the band of audio signals being translated of the type achieved in the prior art by placing two different length lines side by side.

Special structure is necessary to transmit the rotary wave motion past the fold, and comprises the zigzag spring member 22 with elements on either side of told 14 disposed in a plane to present high stifiness to the rotary motion tending to twist the plane but substantially matching the impedance of the line by use of wire of the same dimension in the zigzag spring configuration. At the fold 14 the coupling member is a substantially V- shaped portion with a small coil spring 23 engaging its crotch and linking it to the support member 21. This small coil spring 23 provides a rotational compliance so that the planar member will pivot or roll with the rotational mode of wave transmission about the point of the crotch and transmit the motion across the told from one spring portion 10, 12 to the other.

Each coil spring delay line 141, 12 has an end member 25 extending diametrically across the end of the coil 13 and firmly engaging, such as by a solder joint, an attached sleeve or crimped wire, the fiat plane zig-zag coupling spring 22 at its central axis 26 for transmitting the rotary motion to twist the plane about its axis. This permits the weaker spring rotational compliance member 23 to let the V-shaped fold 1d rotate freely and transfer the rotational component of Wave motion to the opposite delay line coil spring portion 10 or 12. In this way the acute angle of the V fold 14 between the springs can be small to transmit almost pure rotational energy and to make the two delay line portions 10, 12 substantially parallel. It is noted that this flat plane spring coupling member provides a third serially connected length of line and may present a slightly different impedance enhancing the multiple delay characteristic to decrease flutter and to provide a more uniform band pass characteristic.

With this line the performance and response has been found equivalent to straight spring lines and Without significant flutter noise, and yet affording the various advantages of this invention including compactness, fidelity and simplicity.

It is evident from the teachings of this invention, which depart from conventional prior art devices, that certain equivalent devices may be used without departing from the spirit or scope of the invention which is set forth with particularity in the appended claims.

What is claimed is:

1. In a reverberation device of the type employing a coiled spring member having a transmitting transducer at one end producing a rotational component of motion into the spring and a receiving transducer at the other end to receive the rotational component of motion after it has passed through the length of the spring, the improvement comprising in combination a compliance support damped to reduce compressional mode flutter in the spring engaging the spring at at least one intermediate position to produce at least one sharp fold in the spring member at the intermediate engagement position, thereby providing two spring portions with their axes on opposite sides of the fold nearly parallel and with the two ends of the spring and their corresponding transducers located at positions substantially adjacent the axis of the folded spring member, said spring portions providing respective acoustic lengths and impedances for desired bandpass characteristics, and a coupling member encompassing said sharp fold comprising planar elements presenting high stiffness to said rotational component of motion thereby transmitting it through said fold and having an impedance longitudinally substantially matching the impedance of the coiled spring extending from the coupling member on either side of the sharp fold.

2. A system as defined in claim 1 wherein the two spring portions on either side of the fold have different effective lengths along their respective axes chosen of such dimension to provide an improved band pass characteristic over a band of audio frequencies.

3. A system as defined in claim 1 wherein the support is coupled to the coiled spring with a movable member providing a damped compliance for compressional mode flutter by exerting a bi-directional force substantially along the axes of both portions of the coil spring.

4. A reverberation device of the type employing a coiled spring member transmitting wave motion in a rotational mode along the spring from one end to the other having said coiled spring member folded to form at least two substantially parallel spring portions and a support device engaging the spring member at the fold, wherein the coil spring is coupled to said support by an intermediate member providing rotational compliance between the coil spring portions and the support with a rotational compliance magnitude less than that of the coil spring.

5. A system as defined in claim 1, wherein the coupling member is V-shaped and formed of generally zig-zag spring elements with stiff thin plane compliance and a small coil spring to pivot said thin plane on each side of said fold thereby transmitting said rotational motion from one end of the folded spring to the other.

6. A system as defined in claim 5 with a pivoted connection on said support device engaging the small coil spring in the crotch of the V-shaped coupling member.

References Cited UNITED STATES PATENTS 2,768,235 10/1956 Knoblaugh 179-1 2,853,145 9/1958 Martin 181-31 2,982,819 5/1961 Meinema et al. 179-1 3,048,072 8/1962 Hanert 84-124 3,106,610 10/1963 Young et al. 179-1 3,281,724 10/1966 "chafft -1 333-30 HERMAN KARL SAALBACH, Primary Examiner.

C. BARAFF, Assistant Examiner. 

